1. Field of the Invention
The present invention relates to a method for manufacturing a substrate having built-in components in which at least one circuit component is embedded in a resin layer.
2. Description of the Related Art
Recently, as a result of the trend toward reducing the size of electronic apparatuses, a reduction in the size of circuit substrates which are used to mount circuit components, such as a chip capacitor, has been required. In response, the reduction in the size of circuit substrates has been achieved by embedding circuit components in a circuit substrate to form a module so that the mounting areas of the circuit components are reduced. Since a substrate having built-in components in which circuit components are embedded in a resin substrate is lightweight and is not subjected to high temperature firing, unlike a ceramic substrate, there is an advantage in that the type of circuit component to be embedded in the substrate is not particularly limited.
In Japanese Unexamined Patent Application Publication No. 11-220262, a method for manufacturing a substrate having built-in components is disclosed in which after circuit components are mounted on a metal foil with conductive adhesives interposed therebetween, and a resin sheet made of an inorganic filler and a thermosetting resin is disposed on and pressure bonded to the metal foil, the resin sheet is thermally cured to form a resin layer in which the circuit components are embedded therein, and subsequently the metal foil is processed to form a wiring pattern.
However, in the manufacturing method described above, when the circuit components are mounted, or the resin sheet is pressure bonded, since the conductive adhesives are spread in a primary surface direction of the metal foil, the conductive adhesives are brought into contact with each other or are brought into contact with adjacent wiring patterns, so that a short circuit may occur. The same problem also occurs when a solder is used instead of the conductive adhesive. For example, when reflow soldering is performed to mount circuit components, since a melted solder is spread in a primary surface direction of the metal foil, a short circuit may occur between adjacent lands. In particular, when a substrate having built-in components is formed to have a multilayer structure, since heat generated in a reflow process is applied a plurality of times to a circuit component which is mounted first, a solder is re-melted, so that solder spreading may occur.
In Japanese Unexamined Patent Application Publication No. 2005-26573, a method for manufacturing a substrate having built-in components is disclosed in which an insulating layer having opening portions is formed on one primary surface of a metal foil so as to prevent the spread of solder or a conductive adhesive.
FIGS. 9A to 9E show an example of the method for manufacturing a substrate having built-in components disclosed in Japanese Unexamined Patent Application Publication No. 2005-26573. Hereinafter, with reference to FIGS. 9A to 9E, a conventional method for manufacturing a substrate having built-in components will be described.
As shown in FIG. 9A, an insulating layer 52 having opening portions 52a is formed on a metal foil 51 so that the metal foil 51 is partially exposed through the opening portions 52a. 
Next, as shown in FIG. 9B, solder 53 is filled in the opening portions 52a. 
Next, as shown in FIG. 9C, a circuit component 54 is disposed on the insulating layer 52 so that terminal electrodes 54a of the circuit component 54 are brought into contact with the solder 53, and the solder 53 are connected to the terminal electrodes 54a by soldering.
Next, as shown in FIG. 9D, a resin sheet made of an inorganic filler and a thermosetting resin is disposed on and pressure bonded to the insulating layer 52 and the circuit component 54, so that a resin layer 55 in which the circuit component 54 is embedded is formed. In addition, when the resin layer 55 is formed, a metal foil 56 arranged at a rear surface side is simultaneously bonded thereto.
Finally, the front and rear metal foils 51 and 56 are processed, so that wiring patterns 51a and 56a are formed.
In the above-described manufacturing method, the opening 52a formed in the insulating layer 52 functions as an enclosure to prevent the spread of the solder 53. However, since the solder 53 or a conductive adhesive must be filled in the opening portion 52a, a relatively large amount of solder or conductive adhesive is required. In particular, when a solder is used, since the amount thereof is large, solder flow is very likely to occur, and thus, a reliability problem may arise. In addition, when the resin layer 55 and the insulating layer 52 are made of different materials, an adhesion strength therebetween will decrease at the interface, and thereby solder flow may be generated. In recent years, as a result of the trend toward reducing the size and increasing the density, the distance between lands which mount a component embedded in a substrate having built-in components has been significantly decreased. Thus, a high solder-flow resistance is required.